The present invention relates, in general, to releasable seals for cartons, and more particularly to a glue release structure for cigarette cartons or similar products, and methods for releasably sealing a carton which must be sealed closed and later reopened without damage to the carton.
Cigarettes are conventionally packaged in packs of 20, with the packs then being placed in cartons of 10 packs by the manufacturer. These cartons are then placed in cases for shipping by the manufacturer to distributors in various states. Since most states collect a tax on the cigarettes which are sold there, each of the cartons must be opened and the state tax stamp placed thereon before they can be sold at retail outlets. Accordingly, the manufacturer must close and seal the cigarette cartons in such a way that they can be readily opened for placement of the tax stamp on the ends of the packs contained in the carton. This reopening of the cartons must be done in such a way, however, that the cartons are not damaged, for if the carton flaps are torn or if a fiber layer is removed, jamming usually occurs in the tax stamping machinery, causing damage to the cigarettes.
The cartons are conventionally formed from carton blanks which include end flaps and a top closure flap. The end flaps are glued together by for example, a polyvinyl acetate emulsion adhesive during the formation of the carton, and this adhesive forms a permanent bond with the carton material. However, the top closure flap cannot be sealed with the end flap adhesive, since attempts to reopen flaps which are secured by this adhesive often results in tearing of the carton fibers. The opening of the carton to allow the application of tax stamps to the cigarette packs in the carton normally is done by jobbers and wholesalers who are licensed by the particular state for this purpose. Since the manufacturer has no control over these individuals, it is necessary to provide a carton which can easily be opened and then resealed without damage.
After the cartons have been filled with cigarette packs by the manufacturer, they must be conveyed to a further packaging station and placed in cases for shipment. Thus, the top flaps of the cartons must be closed and sealed with an adhesive that is sufficiently strong to withstand the necessary handling without opening, yet must be easily reopenable by the jobbers or wholesalers who must place the state tax stamps on the cigarette packs without damage to the carton so that the carton can be resealed for sale. To accomplish this, the top flaps of cigarette cartons presently are sealed with an adhesive which, upon drying, can be fractured so that it will not tear the fibers of the package when the seal is broken but which is strong enough to hold the carton closed during handling. A crystalline glue is used for this purpose.
Typically, the crystalline glue is applied to a sealing surface on the carton, usually on a closure flap which extends the length of the carton, before or after the carton is filled with ciagarette packs. A carton top flap is then folded over the closure flap and when they are brought into contact with each other, the glue temporarily holds the carton in its closed condition. The use of a special crystalline glue or other special adhesive, e.g. hot melt, for this purpose requires that two kinds of glue be applied to the carton blank, however, one kind for the top flap and another kind for the end flaps, thus requiring two adhesive distribution systems and maintenance of two inventories. Furthermore, in order to prevent accidental bonding of the closure flap a coagulating agent is added to the top flap glue. As a result, if the closure flap and end flap glues should become mixed together, the mixture will cease to function as an adhesive. This insures that any end flap adhesive which might inadvertently find its way onto the top flap won't produce a permanent bond between the top flap and the carton surface to which it is to be sealed.
Crystalline glues dry rapidly following application to carton surfaces. This results in a substantial amount of waste in the manufacturing process, since if a carton is not closed within two minutes after glue application, the carton must be rejected. Furthermore, the coagulating agent causes waste disposal problems. Thus, although crystalline glues have the advantage of being easily fractured so that the seal between the top flap and the carton surface to which it is adhered can be readily broken, the use of a special top flap adhesive is expensive and is hard to work with on carton machines, so there are numerous disadvantages to the use of such an adhesive. Accordingly, an improved solution to the problem of providing an easily openable cigarette carton has long been sought.